Randon suffixs or prefixes would avoid name clashes. You want to avoid the possibilty of overwriting peoples files. This can also be mitigated with a waring to the user with "Overwrite? [y/n]". I like the idea of letting a user set their own custom name too, then people can name their files something useful. Also will the json data contain a name and/or description field? I can imagine creating a lot of simulations, saving them to disk, and then not know what each one is. So something to help keep that in order is needed.